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Strains of Salmonella enterica serovar Typhimurium LT2 lacking a functional 2-methylcitric acid cycle (2-MCC) display increased sensitivity to propionate. Previous work from our group indicated that this sensitivity to propionate is in part due to the production of 2-methylcitrate (2-MC) by the Krebs cycle enzyme citrate synthase (GltA). Here we report in vivo and in vitro data which show that a target of the 2-MC isomer produced by GltA (2-[MC.sup.ltA]) is fructose-l,6-bisphosphatase (FBPase), a key enzyme in gluconeogenesis. Lack of growth due to inhibition of FBPase by 2-[MC.sup.GltA] was overcome by increasing the level of FBPase or by micromolar amounts of glucose in the medium. We isolated an fbp allele encoding a single amino acid substitution in FBPase (S123F), which allowed a strain lacking a functional 2-MCC to grow in the presence of propionate. We show that the 2-[MC.sup.gltA] and the 2-MC isomer synthesized by the 2-MC synthase (PrpC; 2-[MC.sup.PrpC]) are not equally toxic to the cell, with 2-[MC.supGltA] being significantly more toxic than 2-[MC.sup.PrpC]. This difference in 2-MC toxicity is likely due to the fact that as a si-citrate synthase, GltA may produce multiple isomers of 2-MC, which we propose are not substrates for the 2-MC dehydratase (PrpD) enzyme, accumulate inside the cell, and have deleterious effects on FBPase activity. Our findings may help explain human inborn errors in propionate metabolism. doi: 10.1128/JB.01301-09

Feed and energy intake of ruminant animals can change dramatically in response to changes in diet composition or metabolic state, and such changes are poorly predicted by traditional models of feed intake regulation. Recent work suggests that temporal patterns of fuel absorption, mobilization, and metabolism affect feed intake in ruminants by altering meal size and frequency. Research with nonruminants suggests that meals can be terminated by signals carried from the liver to the brain via afferents in the vagus nerve and that these signals are affected by hepatic oxidation of fuels and generation of ATP. We find these results consistent with the effects of diet on feed intake of ruminants. Of fuels metabolized by the ruminant liver, propionate is likely a primary satiety signal because its flux to the liver increases greatly during meals. Propionate is utilized for gluconeogenesis or oxidized in the liver and stimulates oxidation of acetyl CoA. Although propionate is extensively metabolized by the ruminant liver, there is little net metabolism of acetate or glucose, which may explain why these fuels do not consistently induce hypophagia in ruminants. Lactate is metabolized in the liver but has less effect on satiety, probably because of greater latency for reaching the liver within meals and because of less hepatic extraction compared with propionate. Hypophagic effects of fatty acid oxidation in the liver are likely from delaying hunger rather than promoting satiety because [beta]-oxidation is inhibited during meals by propionate. A shortage of glucose precursors and increased fatty acid oxidation in the liver for early lactation cows lead to a lack of tricarboxylic acid (TCA) cycle intermediates, resulting in a buildup of the intracellular acetyl-CoA pool and export of ketone bodies. In this situation, hypophagic effects of propionate are likely enhanced because propionate entry into the liver provides TCA cycle intermediates that allow oxidation of acetyl-CoA. Oxidizing the pool of acetyl-CoA rather than exporting it increases ATP production and likely causes satiety despite the use of propionate for glucose synthesis. A better understanding of metabolic regulation of feed intake will allow diets to be formulated to increase the health and productivity of ruminants. Key words: hepatic vagus, hypophagia, lipolytic state, propionate

ABSTRACT The topical vitamin [D.sub.3] modulator calcitriol, the naturally occurring active form of vitamin [D.sub.3], has long been used for topical psoriasis therapy in Europe and other countries and was [...]

Butane monooxygenase (BMO) catalyses the oxidation of alkanes to alcohols in the alkane-utilizing bacterium 'Pseudomonas butanovora'. Incubation of alkane-grown 'P. butanovora' with butyrate or propionate led to irreversible time- and [O.sub.2]-dependent loss of BMO activity. In contrast, BMO activity was unaffected by incubation with lactate or acetate. Chloramphenicol inhibited the synthesis of new BMO, but did not change the kinetics of propionate-dependent BMO inactivation, suggesting that the propionate effect was not simply due to it acting as a repressor of BMO transcription. BMO was protected from propionate-dependent inactivation by the presence of its natural substrate, butane. Although both the time and [O.sub.2] dependency of propionate inactivation of BMO imply that propionate might be a suicide substrate, no evidence was obtained for BMO-dependent propionate consumption, or [sup.14]C labelling of BMO polypeptides by [[2-.sup.14]C]propionate during inactivation. Propionate-dependent BMO inactivation was also explored in mutant strains of 'P. butanovora' containing single amino acid substitutions in the x-subunit of the BMO hydroxylase. Propionate-dependent BMO inactivation in two mutant strains with amino acid substitutions close to the catalytic site differed from wild-type (one was more sensitive and the other less), providing further evidence that propionate-dependent inactivation involves interaction with the BMO catalytic site. A putative model is presented that might explain propionate-dependent inactivation of BMO when framed within the context of the catalytic cycle of the closely related enzyme, soluble methane monooxygenase.

The anaerobic soil bacterium Eubacterium barkeri catabolizes nicotinate to pyruvate and propionate via a unique fermentation. A full molecular characterization of nicotinate fermentation in this organism was accomplished by the following results: (i) A 23.2-kb DNA segment with a gene cluster encoding all nine enzymes was cloned and sequenced, (ii) two chiral intermediates were discovered, and (iii) three enzymes were found, completing the hitherto unknown part of the pathway. Nicotinate dehydrogenase, a (nonselenocysteine) selenium-containing four-subunit enzyme, is encoded by ndhF (FAD subunit), ndhS (2 x [2Fe-2S] subunit), and by the ndhL/ndhM genes. In contrast to all enzymes of the xanthine dehydrogenase family, the latter two encode a two-subunit molybdopterin protein. The 6-hydroxynicotinate reductase, catalyzing reduction of 6-hydroxynicotinate to 1,4,5,6-tetrahydro-6oxonicotinate, was purified and shown to contain a covalently bound flavin cofactor, one [[2Fe-2S].sup.2+/1+] and two [[4Fe-4S].sup.2+/1+] clusters. Enamidase, a bifunctional Fe-Zn enzyme belonging to the amidohydrolase family, mediates hydrolysis of 1,4,5,6-tetrahydro6-oxonicotinate to ammonia and (S)-2-formylglutarate. NADH-dependent reduction of the latter to (S)-2-(hydroxymethyl)glutarate is catalyzed by a member of the 3-hydroxyisobutyrate/ phosphogluconate dehydrogenase family. A [4Fe-4S]-containing serine dehydratase-like enzyme is predicted to form 2-methyleneglutarate. After the action of the coenzyme [B.sub.12]-dependent 2-methyleneglutarate mutase and 3-methylitaconate isomerase, an aconitase and isocitrate lyase family pair of enzymes, (2R,3S)-dimethylmalate dehydratase and lyase, completes the pathway. Genes corresponding to the first three enzymes of the E. barkeri nicotinate catabolism were identified in nine Proteobacteria.

The effects of pH, acetate, propionate, or butyrate concentration, and diet on acid resistance of fecal Escherichia coli and E. coli O157:H7 were determined by in vitro and in vivo experiments. The pH tested was from 4.0 to 8.0, and the VFA concentrations tested were 0 to 100 mM. The E. coli O157:H7 used was strain 505B. In an in vivo study, cattle were fed a grain-based diet, then either not switched or switched to a grain-based diet with 3% added calcium carbonate or two fiber-based diets (soybean hulls or hay). Acid resistance was expressed as viability after acid-shock at pH 2.0 for 1 h and 4 h for fecal E. coli and E. coli O157:H7, respectively. Enumeration methods used were multitube fermentation, agar plate, and petri-film methods. The E. coli O157:H7 was not found in continuous culture inocula or in vivo samples. The viability of fecal E. coli decreased linearly (P < 0.01) as the culture pH increased, and viability ofE. coli O157:H7 was highest (P < 0.01) when cultivated at pH 6.0. The viability of fecal E. coli and E. coli O157:H7 showed quadratic responses (P < 0.05) as acetate and butyrate concentrations increased at pH 7.2, with maximal acid resistance at 20 and 12 mM, respectively. As propionate concentration increased, the acid resistance was not different (P > 0.05) for fecal E. coli. Acid resistance of E. coli was induced by acetate and butyrate, even though the environmental pH was near neutral. Similar results were measured in the in vivo study, where viability after acid shock was more dependent on VFA concentration than on pH. Increasing the dietary calcium carbonate concentration also increased (P < 0.05) acid resistance of fecal E. coli. Results from these studies demonstrated that culture pH and VFA affect acid resistance of E. coli. Key Words: Diet, Escherichia coli, pH, Resistance, Volatile Fatty Acids

Two experiments were conducted to evaluate how dose-response effects of intraruminal infusion of propionate on feeding behavior and plasma metabolites are altered by diets differing in fermentability. Twelve ruminally cannulated Holstein cows were used in each experiment. Cows were fed diets containing either steam flaked corn or dry cracked corn (30% of dietary dry matter) in expt. 1, and diets differing in forage-to-concentrate ratio (66:34 vs. 36:64) in expt. 2. For both experiments, the experimental design was a crossover for dietary treatment, and a 6 x 6 Latin square for infusion treatment within a diet for each period. Infusion treatments were mixtures of sodium propionate and sodium acetate, containing propionate at 0, 0.2, 0.4, 0.6, 0.8 and 1.0 as a fraction of total volatile fatty acids infused. Treatment solutions were infused into the rumen continuously for 18 h starting 6 h before feeding at a rate of 23.1 mmol/min. Although propionate production from ruminal fermentation was expected to be different, dietary treatments did not affect dry matter intake (DMI) responses to propionate infusion for either experiment. However, propionate infusion decreased DMI linearly in expt. 1, but did not decrease DMI at lower rates of propionate infusion, which were much more effective at increasing plasma glucose concentration in expt. 2. Propionate had a smaller hypophagic effect at low concentrations of plasma glucose and had a greater hypophagic effect at elevated concentrations of plasma glucose, which could be explained by changes in the metabolism of propionate in the liver. J. Nutr. 133: 1105-1112, 2003. KEY WORDS: * propionate infusion * threshold response * plasma glucose concentration * hepatic oxidation

The objective of this experiment was to determine interactions between hypophagic effects of propionate and ammonium in lactating dairy cows. Eight ruminally cannulated Holstein cows in mid-lactation were used in a duplicated 4 x 4 Latin square design experiment with a 2 x 2 factorial arrangement of treatments. Factors evaluated were type of volatile fatty acid (VFA; acetate vs. propionate) and type of salt (sodium vs. ammonium). Treatment solutions were infused continuously into the rumen at a rate of 16.7 mmol of VFA salts/min starting 2 h before feeding and ending 12 h after feeding. Hypophagic effects of ammonium were significantly greater for cows infused with propionate (4.3 vs. 12.1 kg/12 h; SEM = 1.3) compared with acetate (13.5 vs. 15.3 kg/12 h; SEM = 1.3; interaction P < 0.01). This interaction was attributed to a greater reduction in meal frequency for ammonium treatment compared with sodium treatment when infused with propionate (3.9 vs. 7.2/12 h; SEM = 0.8) compared with acetate (6.6 vs. 7.0/12 h; SEM = 0.8), indicating that infusion of ammonium propionate reduced hunger. Meal size was decreased by infusion of propionate compared with acetate, but was not affected by ammonium compared with sodium, indicating that ammonium did not affect satiety. Mechanisms to explain the interactions between ammonium and propionate on meal frequency and feed intake warrant further investigation. J. Nutr. 133: 1100-1104, 2003. KEY WORDS: * propionate infusion * ammonium * urea synthesis * feeding behavior * dairy cows

The dose-response effects of intraruminal infusion of propionate on feeding behavior of lactating dairy cows were evaluated with eight ruminally cannulated Holstein cows past peak lactation. Treatments were mixtures of propionic acid and acetic acid containing propionic acid at eight different concentrations in Experiment 1, and mixtures of sodium propionate and sodium acetate containing sodium propionate at 4 different concentrations in Experiment 2. Experimental designs were an 8 x 8 and duplicated 4 x 4 Latin squares, respectively, for Experiments 1 and 2. Treatment solutions were infused into the rumen continuously for 14 h at a rate of 16.7 and 25 mmol/min, respectively, for Experiments 1 and 2. Infusion started 2 h before feeding and ended 12 h after feeding; feeding behavior was monitored for 12 h after feeding using a computerized data acquisition system. Total metabolizable energy (ME) intake was calculated by adding the energy of infusates to dietary energy intake. In both experiments, as the proportion of propionate of the infusates increased, total ME intake and dry matter intake decreased linearly. As infusion of propionate increased, meal size tended (P < 0.09) to decrease linearly and intermeal interval tended (P < 0.07) to increase linearly in Experiment 1; meal size decreased linearly and number of meal bouts tended (P < 0.08) to decrease linearly in Experiment 2. These observations indicate that the reduction in dietary energy intake from propionate infusion was greater than the energy supplied from infusates, and that propionate plays an important role in feed intake regulation by affecting both satiety and hunger. J. Nutr. 133: 1094-1099, 2003. KEY WORDS: * propionate infusion * feed intake * feeding behavior * dairy cow, dlact

Normal cardiac metabolism requires continuous replenishment (anaplerosis) of catalytic intermediates of the citric acid cycle. Little is known about the quantitative aspects of propionate as a substrate of in vivo anaplerosis; therefore, we measured the rate of propionate entry into the citric acid cycle in hearts of anesthetized pigs. [U-[sup.13][C.sub.3]]propionate (0.25 mM) was infused in a coronary artery branch for I h via an extracorporeal perfusion circuit, and cardiac biopsies were analyzed for the mass isotopomer distribution of citric acid cycle intermediates. Infusion of propionate did not affect myocardial oxygen consumption, heart rate, or contractile function. In the infused territory, propionate infusion did not affect uptake of glucose and lactate but decreased free fatty acid uptake by one-half (P < 0.05). Propionate extraction and uptake were 57.4 [+ or -] 3.3% and 0.078 [+ or -] 0.009 [micro]mol * [min.sup.-1] * [g.sup.-1]. Anaplerosis from propionate, calculated from the mass isotopomer distribution of succinate, accounted for 8.9 [+ or -] 1.3% of the citric acid cycle flux. Propioylcarnitine release accounted for only 0.033 [+ or -] 0.002% of propionate uptake. Methylcitrate did not accumulate. Thus administration of a low concentration of propionate appears to be a convenient and safe way to boost anaplerosis in the heart. tricarboxylic acid cycle; cataplerosis; mass isotopomer analysis; mass spectrometry

An experiment was conducted to evaluate the dietary effects of Cr propionate (CrProp) and metabolizable energy (ME) on growth, carcass traits, and pork quality of growing-finishing pigs. One hundred forty-four Cambrough-22 barrows were allotted to four dietary treatments in a randomized complete block design (six replicates of six pigs per replicate; average initial and final body weight were 27 and 113 kg, respectively). The dietary treatments were: 1) corn-soybean meal basal (B; low ME), 2) B + 200 ppb of Cr (as CrProp), 3) B + 200 kcal ME/kg (4.5% added fat; high ME), or 4) B + 200 kcal ME/kg + 200 ppb of Cr. At trial termination, three pigs per replicate were killed to determine dietary effects on carcass traits and pork quality. Overall average daily gain, average daily feed intake, and gain:feed ratio were not affected (P > 0.10) by diet. During the early growing period, average daily gain was increased in pigs fed the CrProp-low-ME diets, but decreased in pigs fed the CrProp-high ME diets (Cr x ME, P < 0.04). Feed intake was increased (P < 0.05) in pigs fed the high-ME diets during the early growing period. Forty-five min and 24 h pH were not affected (P > 0.10) by diet. The CIE L * tended (P = 0.07) to be increased and shear force tended (P = 0.06) to be decreased in pigs fed high-ME diets. Subjective marbling was increased (P < 0.03) and longissimus muscle percentage moisture and thaw loss were decreased (P < 0.04) in pigs fed CrProp. Chromium propionate had no consistent effect on growth and carcass traits in this experiment; however, CrProp did affect some aspects of pork quality. Key Words: Chromium, Metabolizable Energy, Pigs, Pork, Propionic Acid, Quality

Results demonstrate that propionate utilization by activated sludge organisms, in enhanced biological phosphorus removal systems, occurs via succinate dehydrogenase under anaerobic conditions. Data show that 3-(sup)13C-labeled propionate labels carbon C-3 of hydroxyvalerate, indicating the operation of tricarboxylic acid cycle.

The current study examined the acute effects of intravenous propionate infusion on plasma hormones and metabolites and the expression of adipose tissue lipogenic genes. Four yearling rams were assigned to one of two groups (saline or propionate infusion) in a crossover design. All sheep were cannulated in both jugular veins and infused with 1.2 M propionate at a rate of 64 [micro]mol*[min.sup.-1]*kg B[W.sup.-1] for 30 min. Blood samples were collected at -10, 0, 5, 10, 20, 30, 60, and 120 min after initiation of infusion. Subcutaneous adipose tissue biopsies were obtained from the tailhead at 0 and 2 h after propionate infusion and analyzed for gene expressions of lipoprotein lipase, acetyl CoA carboxylase, fatty acid synthase, peroxisome proliferator-activated receptor [gamma], leptin, and uncoupling protein-2 using a nonisotopic ribonuclease protection assay. The partial cDNA of the enoyl reductase region of ovine fatty acid synthase was cloned and sequenced from s.c. adipose tissue of sheep. The deduced amino acid sequence (210 amino acids) was 86% identical to human, 88% identical to rat, 88% identical to mouse, and 72% identical to chicken. Plasma glucose and insulin concentrations abruptly increased 5 min after beginning propionate infusion and further increased up until 30 min but were unaffected in saline-infused sheep (P < 0.05). Plasma concentration of NEFA decreased (P < 0.05) during propionate infusion, whereas IGF-I levels were unaltered. The amounts of lipoprotein lipase, acetyl CoA carboxylase, fatty acid synthase, peroxisome proliferator-activated receptor [gamma], and leptin mRNA increased (P < 0.05) in s.c. adipose tissue of propionate-infused sheep compared with those of saline-infused sheep. However, uncoupling protein-2 mRNA decreased (P < 0.05) in propionate-infused sheep. This study demonstrates that an acute nutrient challenge, in the form of i.v. propionate, can stimulate or inhibit the expression of various adipose tissue genes involved with lipogenesis and adipose tissue metabolism. Key Words: Adipose Tissue, Complementary DNA, Fatty Acid Synthase, Lipogenesis, Propionate, Sheep

To investigate the metabolism of 1,2-propanediol (PPD) in lactating cows independently of normal rumen microbial metabolism, three ruminally cannulated lactating Holstein cows were subjected to three experimental infusion protocols under washed reticulo-ruminal conditions in a Latin square design. Reticulo-ruminal absorption rates were maintained for 420 min by continuous intraruminal infusion of VFA and PPD. With the control treatment, 1,246 [+ or -] 39 mmol/ h of acetate and 213 [+ or -] 5 mmol/h of butyrate were absorbed from the reticulorumen. With the propionate treatment, 1,148 [+ or -] 39 mmol/h of acetate, 730 [+ or -] 23 mmol/ h of propionate and 196 [+ or -] 5 mmol/h of butyrate were absorbed from the reticulorumen. With PPD treatment, 1,264 [+ or -] 39 mmol/h of acetate, 220 [+ or -] 5 mmol/h of butyrate and 721 [+ or -] 17 mmol/h of PPD were absorbed from the reticulorumen. Glucose irreversible loss rate (ILR), as well as the relative enrichment of plasma lactate and alanine, were determined by primed continuous infusion of [U-[sup.13]C]glucose in a jugular vein. Treatments did not affect (P > 0.10) the plasma concentrations of glucose (4.2 [+ or -] 0.1 mmol/L), alanine (0.14 [+ or -] 0.01 mmol/L), or insulin (80 [+ or -] 25 pmol/L). The plasma concentration of lactate was higher (P < 0.05) with both propionate (0.84 [+ or -] 5 mmol/L) and PPD treatment (0.81 [+ or -] 5 mmol/ L) compared with the control treatment (0.29 [+ or -] 0.5 mmol/L). The plasma concentration of pyruvate was higher (P < 0.05) with the propionate treatment (0.09 [+ or -] 0.01 mmol/L) compared with the control treatment (0.03 [+ or -] 0.01 mmol/L). The plasma concentration of 3-hydroxybutyrate was lower (P < 0.05) with the propionate treatment (0.15 [+ or -] 0.03 mmol/L) compared with the control treatment (0.40 [+ or -] 0.03). With the PPD treatment, the plasma concentrations of pyruvate and 3-hydroxybutyrate were in between the other treatments and tended (P < 0.10) to be different from both. The plasma concentration of PPD increased throughout the infusion period with the PPD treatment and reached a concentration of 4.9 [+ or -] 0.6 mmol/L at 420 min. The ILR of glucose was not affected (P > 0.10) by treatments (441 [+ or -] 35 mmol/h). The relative [sup.13]C enrichment of plasma lactate compared with that of glucose decreased (P < 0.05) with the PPD treatment compared with the control treatment (44 to 21 [+ or -] 3%). It was concluded that PPD has a low rate of metabolism in cows without a normal functioning rumen, although about 10% of the absorbed PPD was metabolized into lactate. Key Words: Dairy Cattle, Gluconeogenesis, Metabolism, Propionic Acid, Propylene Glycol, Ruminants

Research has been conducted on the propionyl-CoA biosynthesis pathway in Salmonella enterica recombinant strain. The reconstitution of this pathway has been carried out and the results indicate that this heterologous pathway converts succinyl-CoA to propionyl-CoA.

Research has been conducted on Corynebacterium glutamicum genome. The identification, cloning and molecular characterization of C. glutamicum citrate synthase homologous genes located in different gene clusters have been carried out and the cluster responsible for the propionate degradation has been determined.

Research has been conducted on autotrophic CO (sub)2 fixation pathway in Chloroflexus aurantiacus. The NADPH-dependent reduction of malonyl-CoA to 3-hydroxypropionate in C. aurantiacus has been investigated and the results indicate that this enzyme may be used for 3-hydroxypropionate production.

Research demonstrates that the conserved amino acid residue K592 of the propionyl-CoA synthetase of Salmonella enterica mediates adenylate formation as well as supports the growth of the bacterium on propionate. Further, the residue does not play a role in thioester bond formation.

Transposon5 mutagenesis studies reveal that in Ralstonia eutropha HF39, propionic acid metabolism is mediated by the methylcitric acid pathway. Data indicate that genes of the pathway occur in a cluster with prpR gene transcribing a gene product of approximately 71 kilodalton.

Research has been conducted on the macrolide antibiotics oligomycin C and rutamycin B. The results of the convergent asymmetric syntheses of these antibiotics which share a common ring system and an identical polypropionate fragment bearing stereogenic centers are reported.

Research delineates the gene expression, regulation, and enzyme properties of phosphoenolpyruvate carboxykinase (Pck) and pyruvate kinase (Pyk) in the methanogenic bacterium Selenomonas ruminantium. Results show that both pck and pyk genes are monocistronic with varying amounts of mRNA production, which is affected by the energy substrate.

Research conducted on the effect of acetate and formate/H (sub)2 utilizers on the volatile fatty acids degrading digester seeds is presented. Experiments demonstrate thermodynamic and kinetic transfer implications of acetate regulation.

The role of portal propionate on food intake was analyzed in sheep during feeding protocols to characterize the efficiency of the compound for short-term feed intake-regulation. Infusions of propionate in sheep jugular and mesenteric veins reduced food intake in a dose-dependent manner. Infused propionate also acted as a signal of satiety that was not counteracted during the meal period. However, low levels of propionate infusion had not effect of feeding patterns.

The paracellular permeability of Caco-2 colon cancer cells in response to butyrate, propionate and acetate was analyzed to determine the role of short chain fatty acids (SCFAs) in the regulation of paracellular permeability. The paracellular permeability of Caco-2 cells was reduced after the administration of butyrate, propionate and acetate which also increased transepithelial resistance. However, the effects of the SCFAs on the barrier function of Caco-2 monolayers was reversible and concentration-dependent.

Isolated hepatocytes prepared from sheep fed a basal diet (bromegrass hay-corn, 50:50 wt/wt, as-fed basis) with or without urea were used to determine the effects of added ammonia (as [NH.sub.4]Cl) and propionate on the partitioning of C from 1.25 mM L-[1-14C]alanine between oxidation and gluconeogenesis, and the flux of 15N from 1.25 mM L-[15N]alanine to [14N15N]urea and [15N15N]urea. Hepatocyte suspensions were incubated with [NH.sub.4]Cl (0, .31, .63, and 1.25 mM) and(or) propionate (0, .31, .63, and 1.25 mM) in the presence of either 1.25 mM L-[15N]alanine or 1.25 mM L-alanine plus 18.5 kBq of L-[1-14C]alanine. Feeding dietary urea did not affect [1-14C]alanine oxidation to 14C[O.sub.2] (P = .601), or its conversion to [14C]glucose (P = .576) by isolated hepatocytes. Increasing in vitro concentrations of [NH.sub.4]Cl and propionate between 0 and 1.25 mM reduced [1-14C]alanine oxidation to 14C[O.sub.2] (P < .001). Increasing [NH.sub.4]Cl concentration between 0 and 1.25 mM reduced [1-14C]alanine conversion to [14C]glucose in isolated hepatocytes (P < .001), whereas addition of propionate between 0 and 1.25 mM stimulated production of [14C]glucose from [1-14C]alanine (P < .001). Feeding urea did not affect in vitro rates of total urea production (P = .655) but increased the production of [14N15N]urea and [15N15N]urea (P < .05). Addition of [NH.sub.4]Cl increased total urea, [14[N.sup.15]4N]urea, and [15[N.sup.15]N]urea production (P < .001) but reduced 15N isotopic enrichments of [14N15N]urea and [15N15N]urea (P < .001). Increasing propionate concentration between 0 and 1.25 mM reduced total urea production (P < .001), but [14N15N]urea and [15N15N]urea production was reduced only at 1.25 mM propionate (P < .001). We conclude that [NH.sub.3] detoxification by isolated sheep hepatocytes increases amino acid deamination and this might have implications for nitrogen retention in ruminants consuming diets that promote considerable [NH.sub.3] absorption from the digestive tract. Key Words: Sheep Liver Cells, Amino Acids, Gluconeogenesis, Ureagenesis, Ammonia, Propionate

The biochemical activity of the CobB protein during the biosynthesis of propionate was analyzed in Salmonella typhimurium LT2 strains. The catabolism of propionate was inhibited in Salmonella typhimurium cobB mutants that were cultured in a 1,2-propanediol medium due to the inhibition of CobB proteins. However, the cobB mutants exhibited normal growth in glucose, glycerol, pyruvate and acetate nutrient media.

Propionate decreases fatty acid oxidation by 38% but has no effect on acetate or glucose metabolism in intact working pig hearts during reperfusion after ischemia. However, propionate delays the formation of CO2. The suppression of fatty acid oxidation is not related to the scavenging of CoA or carnitine molecules by propionate. The level of creatine phosphate and adenine nucleotides in hearts with ischemia is similar to that in control hearts. This indicates that the change in substrate preferences does not impair energy metabolism.

Hepatocytes isolated from sheep were incubated in the presence of reduced phenolics and glycine to determine the effects of these compounds on hepatic propionate metabolism in vitro. 3-Phenylpropionic (PPA) or t-cinnamic (CA) acids, but not benzoic (BA) or 3-(4-hydroxyphenyl)propionic (4OHPPA) acids, decreased conversion of propionate to glucose at .05 mM in the absence of supplemental glycine. At 1.2 mM, all reduced phenolics decreased conversion of propionate to glucose in the absence of supplemental glycine. Addition of glycine to the incubation medium linearly alleviated the inhibition by BA, PPA, or CA, suggesting that physiological glycine concentrations limited alleviation of inhibition of propionate metabolism. Hippuric acid production increased as glycine concentration increased in the presence of PPA, CA, or 4OHPPA. Bovine serum albumin did not alleviate inhibition of conversion of propionate to glucose caused by BA, PPA, or CA and slightly alleviated inhibition caused by 4OHPPA (.4 mM). Of the reduced phenolics tested, PPA is the most likely to inhibit gluconeogenesis from propionate in ovine liver in vivo. Key Words: Propionates, Phenolic Acids, Liver Cells, Sheep, Gluconeogenesis

Six crossbred wether lambs were used in a crossover design to determine the effects of a 3-d feed and water deprivation period on metabolite and hormonal response to a propionate load. During each period of the crossover design all lambs were limit-fed (700 g/d) a 36% concentrate diet for 16 d, then three of the six lambs were deprived of feed and water for 3 d. All lambs were then limit-fed (700 g/d) the 36% concentrate diet (realimentation). Propionate loading tests were performed 4 h before feeding on d 1, 5, and 9 of the realimentation period. A 1.84 M propionate solution (3 mmol/kg BW) was infused into the right jugular vein and blood samples were obtained from the left jugular vein at intervals for 4 h after infusion. At the end of the 3-d feed and water deprivation period, fed lambs had greater serum insulin (P [is less than] .02), acetate (P [is less than] .01), and glucose (P [is less than] .05) concentrations and lower plasma-free fatty acids (P [is less than] .01) and urea N (P [is less than] .05) concentrations than unfed lambs. On d 1 of realimentation, previously unfed lambs had greater postinfusion growth hormone (P [is less than] .05), free fatty acid (P [is less than] .01), propionate (P [is less than] .07), lactate (P [is less than] .04), and urea N (P [is less than] .05) concentrations and lower serum insulin (P [is less than] .02), and acetate (P [is less than] .03) concentrations than fed lambs. Serum prolactin concentrations increased (P [is less than] .02) postinfusion in unfed lambs but not in fed lambs. Results of this study are interpreted to indicate that appreciable metabolic adaptations occur during feed and water deprivation but that these metabolic changes are corrected within 5 d of realimentation.

Propionate (0, 1, 2, 4, 8, 16, 32, and 64 |micro~mol|center dot~kg B|W.sup.-1~|center dot~|min.sup.-1~ for 30 min) was infused i.v. to investigate the physiological effects of propionate on insulin and glucagon responses in sheep. An i.v. propionate infusion (32 |micro~mol|center dot~kg B|W.sup.-1~|center dot~|min.sup.-1~ for 30 min) with adrenergic and cholinergic blockades was also conducted to clarify the role of autonomic innervation in the control of propionate-induced insulin and glucagon responses. In the experiment in which we studied responses to propionate infusion, the concentrations of plasma insulin and glucagon during propionate infusion increased (P |is less than~ .05) from the preinfusion concentrations at infusion rates of |is greater than~ 4 and 8 |micro~mol|center dot~kg B|W.sup.-1~ |center dot~|min.sup.-1~, respectively. The incremental response areas of plasma insulin and glucagon during propionate infusion increased (P |is less than~ .05) at infusion rates of |is greater than~ 16 and 32 |micro~mol|center dot~kg B|W.sup.-1~|center dot~|min.sup.-1~, respectively. In the experiment studying the effects of adrenergic and cholinergic blockades on responses to propionate, the insulin incremental response area during propionate infusion was suppressed (P |is less than~ .05) by atropine infusion but it was not influenced by phentolamine, propranolol, or hexamethonium infusions. The glucagon response area was suppressed (P |is less than~ .05) by phentolamine infusion, but it was not influenced by propranolol, atropine, or hexamethonium infusions. It is concluded that in sheep 1) propionate may have a physiological role in stimulating insulin and glucagon responses, 2) the propionate-induced insulin response is partly due to the parasympathetic nervous system through activation of a muscarinic receptor, and 3) the propionate-induced glucagon response is stimulated by adrenergic |Alpha~-receptors.

A cloned human colon was studied for its cell line, HT29-18-C1. The cellular transport mechanisms that were stimulated when exposed to short-chain fatty acids (SCFAs) were studied. It was observed that the nonionic diffusion of SCFAs into HT29 cells stimulates several ionic transport factors to facilitate better means of regulating the cell volume and Na+ concentration within the cell.

Water-soluble fiber diet supplements have been found to lower serum lipids. Colonic fiber fermentation produces short chain fatty acids such as acetate, propionate and butyrate. Propionate inhibits cholesterol synthesis in vitro and may contribute to hypolipidemia. The effect of propionate infusions to the cecum on serum lipids, sterol excretion and nutrient digestibility was studied. The infusions did not lower serum lipid levels but caused a 15% increase in total serum cholesterol and LDL cholesterol. The changes in the other two parameters were not detectable. Propionate absorption appears to have no hypolipidemic effects.

Aims: α1 Antitrypsin was undetectable in several patient samples treated with 0.5% β propiolactone, which was used as a virucidal agent. This study was designed to confirm β propiolactone as [...]

The effects of vitamin B12 on propionate formation and yield by Prevotella ruminicola 23 were examined. Acetate and succinate were the major fermentation products in batch culture in the absence of vitamin B12. On the other hand, propionate and succinate were the predominant fermentation products in continuous culture in the presence of vitamin B12 at low and high dilution rates, respectively. Thus, propionate production, which required vitamin B12, could be an energy conservation mechanism.

Harada, Etsumori, Megumi Mitani, and Takashi Takeuchi. Potentiation of carbachol-induced amylase re]ease by propionate in guinea pig and vole pancreatic acini. Am. J. Physiol. 277 (Regulatory Integrative Comp. Physiol. 46): R767-R775, 1999.--The action of propionate, one of the major end products of microbial fermentation in herbivores was investigated in isolated, perifused pancreatic acini of guinea pigs, voles, and mice. With the use of guinea pig acini, 100 [micro]M propionate had no effect, whereas 300 and 600 [micro]M increased amylase release by six- and ninefold, respectively. Simultaneous perifusion of carbachol (CCh) 10 [micro]M plus propionate 100 [micro]M in guinea pig acini produced a potentiated secretory response that was 130% higher than the summated value obtained with CCh and propionate alone. The potentiation by propionate (100 [micro]M) of CCh (10 [micro]M)-induced amylase release was also obtained in vole pancreatic acini, but the mouse pancreatic preparation did not exhibit a similar potentiation. In contrast to CCh, propionate (100-600 [micro]M) alone had no significant effect on intracellular [Ca.sup.2+] concentration ([[[Ca.sup.2+]].sub.i]) and did not alter [[[Ca.sub.2+]].sub.i] elicited by CCh. Ca ionophore A23187 (5 [micro]M)-induced amylase release in guinea pig acini was enhanced two fold by the addition of propionate. Cellular cAMP content was increased slightly by propionate, but did not alter dose dependently. The cAMP level with combinations of CCh and propionate was almost same as that with CCh alone and propionate alone. Staurosporine did not modify amylase secretion induced by a combination of CCh and propionate. These results suggest that propionate, in addition to a direct action on amylase release, potentiates CCh-induced amylase release in guinea pig and vole acini via a secretory pathway not associated with an increase in [[[Ca.sub.2+]].sub.i] and cellular cAMP. secretory response; adenosine 3',5'-cyclic monophosphate; intracellular Ca ions

The objective of this study was to compare an intermittent dosing regimen of fluticasone propionate (FP) cream 0.05% (twice per week) with its vehicle base in reducing the risk of [...]

Research has been conducted on the complex hexacyclic ring system with the stereocenters and a strained bridgehead alkene. The synthesis of the alkene structure has been carried out and the results are reported.

In this study, a new combination ointment containing both calcipotriol and betamethasone dipropionate was compared to betamethasone dipropionate ointment (Diprosone) and calcipotriol ointment (DovoNex) in patients with psoriasis vulgaris. A [...]